Multipatch antenna with ease of manufacture and large bandwidth

ABSTRACT

A multipatch antenna including radiating patches (2) positioned on a dielectric sheet (1). The patches (2) are capacitively fed by probes (7) ending in the dielectric sheet (1) near the patches (2). By positioning the probes (7) near selected edges of the radiating patches (2), a selected polarization direction of the radiation field can be realized. By positioning several probes (7) near a radiating patch (2), a radiation field with an adjustable polarization direction or a radiation field with an extremely low cross-polarization can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a multipatch antenna comprising an array of atleast substantially equal radiators, positioned on one side of adielectric sheet, a conductive ground plane positioned on the other sideof the dielectric sheet, feeding means positioned near the ground planeon a side facing away from the dielectric sheet and capacitive couplingmeans incorporated between the feeding means and the radiators forenergizing the radiators.

2. Discussion of the Background

A multipatch antenna of this kind is known from EP-A0.449.492. In thisknown multipatch antenna every patch consists of two disc-shapedradiators, disposed parallel and spaced apart, and the capacitivecoupling is provided with a feed and a disc-shaped top capacity.Moreover a capacitive block is located near the radiator as anadditional reactance element. Compound patches of this type areexpensive and do not lend themselves for the production of large arrays.

SUMMARY OF THE INVENTION

The present invention has for its object to realise a multipatch antennathat is easy to be constructed and has a large bandwidth. The antenna ischaracterised in that the radiators each consist of one single radiatingpatch, positioned on an outer surface of the dielectric sheet and thatthe capacitive coupling means comprise constant diameter conductingprobes, on one side connected to the feeding means and on the other sideending in the dielectric sheet near a radiating patch, such that theseprobe ends are completely embedded in the dielectric sheet.

In addition the inventive multipatch antenna can also be excellentlymodelled due to the simple structure and the predictable behaviour ofthe radiating patches. This makes the antenna very suitable forapplications where the selection of the polarization direction of theradiation pattern is desirable. Selection of the polarization is knownper se, for example from the IEE PROCEEDINGS-H, vol 139, no. 5, October1992, pages 465-471, P. S. Hall, "Dual polarization antenna arrays withsequentially rotated feeding".

According to a first embodiment of the present invention, the antenna ischaracterised in that the probes end near selected edges of theradiating patches for generating a radiation pattern with a selectedpolarization direction. The feeding means will mostly be implemented asa transmission-line network, for instance a microstrip network mountedto a second dielectric sheet, which second dielectric sheet is mountedto the ground plane, the microstrip network being mounted on the sidefacing away from the ground plane.

According to a second very favourable embodiment, the antenna ischaracterised in that two probes per radiating patch are provided, bothending near two opposed edges of the radiating patch. Energizing the twoprobes in opposite phases via the transmission line network results in aradiation pattern with a selected polarization direction and a very lowcross-polarization.

On account of its uncomplicated construction and the predictablebehaviour of the radiating patches, the multipath antenna according tothe invention can be conveniently used as a conformal array, forinstance as a skin section of an aircraft. In this application, thepatches are situated on a curved dielectric sheet which forms anintegral part of the fuselage, the feeding means being mounted in theaircraft interior. As known in the art, the feeding means shall bearranged such as to allow for phase differences caused by the curvatureof the antenna plane. Also the polarization behaviour of the antennathus obtained can be excellently modelled due to the predictablebehaviour of the radiating patches.

According to a third embodiment, the feeding means comprise a second,separately feedable transmission line network.

In a first application of this embodiment, the multipatch antenna ischaracterised in that for each radiating patch a first probe is providedfor generating a radiation pattern with a first polarization directionand a second probe for generating a radiation pattern with a secondpolarization direction, which second polarization direction is at leastsubstantially perpendicular to the first polarization direction. Byconnecting the first probe to the first transmission line network andthe second probe to the second transmission line network and bysubsequently feeding both networks in a suitable manner, an antenna withan adjustable polarization direction can be obtained.

In a second application of this embodiment, the antenna is characterisedin that for each radiating patch, a first pair of probes is provided forgenerating a radiation pattern with a first polarization direction and asecond pair of probes for generating a radiation pattern with a secondpolarization direction being at least substantially perpendicular to thefirst polarization direction. The first transmission-line network isthen arranged for feeding the first pair of probes with opposite phasesand the second transmission-line network is arranged for feeding thesecond pair of probes with opposite phases. Thus, an antenna with anadjustable polarization direction and a very low cross-polarization isobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 schematically represents a front view of an existing multipatchantenna and a microstrip-line network;

FIG. 2 schematically represents a side view of an embodiment of themultipatch antenna according to the invention together with amicrostrip-line network;

FIG. 2a schematically represents a side view of an embodiment of themultipatch antenna according to the present invention wherein theantenna is a conformal array antenna on a curved ground plane;

FIG. 3 schematically represents the position of the probes for obtaininga radiation pattern with a horizontal polarization direction;

FIG. 4 schematically represents the position of the probes for obtaininga radiation pattern with a vertical polarization direction;

FIG. 5 schematically represents the position of the probes for obtaininga radiation pattern with a horizontal polarization direction and areduced cross-polarization;

FIG. 6 schematically represents the position of the probes for obtaininga radiation pattern with a vertical polarization direction and a reducedcross-polarization;

FIG. 7 schematically represents a side view of an embodiment of themultipatch antenna according to the invention together with twomicrostrip-line networks;

FIG. 8 schematically represents the position of the probes for obtaininga radiation pattern with an adjustable polarization direction;

FIG. 9 schematically represents the position of the probes for obtaininga radiation pattern with an adjustable polarization direction and anextremely reduced cross-polarization;

FIG. 10 schematically represents a side view of a multipatch antennaconnected to an array of phased array elements;

FIG. 11 schematically represents a side view of a multipatch antennaconnected, via connectors, to an array of phased array elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, and moreparticularly to FIG. 1 thereof, which shows a front view of an existingmultipatch antenna, comprising a dielectric sheet 1 on which radiatingpatches 2(i,j) are mounted in a regular pattern. A transmission-linenetwork 3 connects each radiation patch 2(i,j) to an input terminal 4which, for instance via a coaxial connector not illustrated in thedrawing, may be connected to a transmitter device or to a receiverdevice. Particularly the transmission-line network 3 has beenrepresented in a very simplified manner, since various measureswell-known in he art are required to prevent reflections and also toensure an in-phase drive of all radiating patches 2(i,j). The dielectricsheet 1 is generally mounted to a metal plate not visible in the drawingand is made of a material having low dielectric losses. Although FIG. 1shows a configuration of patches 2(i,j) arranged to lie in rows andcolumns, other configurations are also possible, such as for instance aconfiguration in which the odd-numbered rows are staggered half a columnwith respect to the even-numbered rows. This may prevent the occurrenceof grating lobes.

FIG. 2 shows a side view of an embodiment of a multipatch antennaaccording to the invention. On one side, the dielectric sheet 1comprises a regular pattern of radiating patches 2(i,j) and on the otherside it is provided with a metal plate 5. The transmission-line network3, implemented as a microstrip-line network and provided with an inputterminal 4, is, however, now mounted on a second dielectric sheet 6,which is also positioned on metal plate 5. This transmission-linenetwork 3 may be identical to that shown in FIG. 1, although in view ofthe excess space, its implementation may also differ in detail, such inaccordance with design criteria well-known in the art. Connection of thetransmission-line network 3 to the radiating patches 2(i,j) is,according to the invention, effected by means of probes 7(i,j) which areconnected on one side to the transmission-line network 3 and end on heother side in the dielectric sheet 1, near radiating patch 2(i,j). Thustransmission-line network 3 and radiating patch 2(i,j) are coupledcapacitively. In order to allow the passage of probe 7(i,j), metal plate5 is, where necessary, provided with holes 8, the diameters of which areselected in connection with the diameter of the probes 7(i,j) so as tominimize microwave radiation reflection.

In the present embodiment the diameter of the probes 7(i,j) is 0.8 mmand the diameter of the holes is 1.8 mm. Dielectric sheet 6 is alsoprovided with holes whose diameters correspond with the diameters ofprobes 7(i,j). These holes may be partially metal-plated to effect areliable connection or to obtain improved microwave characteristics. Inaddition, the holes will often be surrounded by short-circuit pins toeffect a proper coupling of the microwave energy in conducting probe7(i,j). Dielectric sheet 1 is provided with blind holes, whose diameterscorrespond with the diameters of probes 7(i,j). In the presentembodiment pertaining to an antenna operating in the 10 GHz frequencyrange, the thickness of the dielectric sheet 1 is 4.2 mm, probe 7(i,j)ending at 0.17 mm from radiating patch 2(i,j). Dielectric sheet 1 mayfor instance be made of Duroid, a material well-known in the art, whichhas a relative dielectric constant of 2.5. If so required, dielectricsheet 1 may comprise a sandwich consisting of two sheets, the first ofwhich is drilled through to allow the passage of probes 7(i,j) and thesecond of which is not drilled for obtaining the specified distancebetween probes 7(i,j) and radiating patches 2(i,j).

In another embodiment the diameter of the probe 7(i,j) is 1.27 mm andthe diameter of the hole is 4.2 mm, the thickness of the dielectricsheet 1 is 6.61 mm and the probe 7(i,j) ends at 0.25 mm from radiatingpatch 2(i,j).

The patch is rectangular with sides of 11.5 mm. The probe ends justunderneath an edge of the patch, 1.15 mm away from a corner. Thisembodiment has at a centre frequency of 7 GHz a -10dB bandwidth of 3.3GHz.

Instead of a microstrip network on a dielectric sheet, transmission-linenetwork 3 may also consist of a sandwich of two dielectric sheets,clamped between two metal plates, the actual transmission line beingpositioned between the dielectric sheets. This construction, which iswell-known in the art, is more complex, but produces a network withlower radiation losses.

For some applications it is recommendable to cover the patches with anadditional dielectric film. Apart from offering a protection againstmechanical and chemical influences, this method may provide, at afavourably selected thickness and dielectric constant of the additionaldielectric film, an additional increase of the antenna bandwidth.

The antenna may also be configured as a conformal array antenna on acurved ground plane as shown in FIG. 2A.

FIG. 3 schematically presents the position of a probe 7(i,j) withrespect to the associated radiating patch 2(i,j) if an antenna with ahorizontal polarization direction is required. By positioning theconducting probe near bet centre of a vertical edge, the patch isexcited such that energy is at least substantially radiated in a desiredpolarization direction. The application of a circular patch is alsopossible, the conducting probe shall then be positioned accordingly. Asa rule, a rectangular patch is more advantageous for horizontal orvertical polarization.

Similarly, FIG. 4 schematically represents the position of probe 7(i,j)with respect to the corresponding radiating patch 2(i,j) if an antennawith a vertical polarization direction is required. By positioning theconducting probe near the centre of a horizontal edge, the patch isexcited such that energy is radiated at least substantially in a desiredpolarization direction.

FIG. 5 schematically represents the position of probes 7(i,j) and7'(i,j) with respect to the corresponding patch 2(i,j) if an antennawith a horizontal polarization direction and an extremely reducedcross-polarization is required. Both vertical edges of the radiatingpatch 2(i,j) are excited in opposite phases via transmission-linenetwork 3, probe 7(i,j) and probe 7'(i,j).

FIG. 6 schematically represents the position of probes 7(i,j) and7'(i,j) such that a vertical polarization direction with an extremelyreduced cross-polarization can be realised analogously.

FIG. 7 represents a side view of an embodiment of the multipatch antennawith a second transmission-line network 9 provided with an inputterminal 4', implemented as a microstrip network mounted on a seconddielectric sheet 10 which is mounted on a second metal sheet 11.Transmission-line network 9 is provided with probes 14(i,j) which, viadielectric sheet 6 and metal plate 5, which is for that purpose providedwith holes 13(i,j), end near radiating patches 2(i,j). This enables eachradiating patch 2(i,j) to be provided with two probes 7(i,j), energizedby transmission-line network 3 and two probes 14(i,j), energized bytransmission-line network 9. Also this network 9 can be realised asstrips clamped between two dielectric sheets and two metal plates or canbe implemented in similar stripline technology.

FIG. 8 schematically represents the position of probes 7(i,j) and14(i,j) with respect to corresponding radiating patch 2(i,j) if anantenna with an adjustable polarization direction is required. Ahorizontal polarization direction can be obtained by feeding radiatingpatch 2(i,j) by transmission-line network 3 and probes 7(i,j) and avertical polarization direction can be obtained by transmission-linenetwork 9 and probes 14(i,j). As well-known in the art, any requiredpolarization direction can then be realised by controlling the phase andamplitude of the microwave energy to be supplied to thetransmission-line networks.

FIG. 9 schematically represents the position of a first pair of probes7(i,j) and 7'(i,j) and a second pair of probes 14(i,j) and 14'(i,j) forobtaining a radiation pattern with an adjustable polarization directionand an extremely reduced cross-polarization. Probes 7(i,j) and 7'(i,j)are fed through transmission-line network 3 in opposite phases andprobes 14(i,j) and 14'(i,j) are fed through transmission-line network 9in opposite phases. Also in this case it is possible to realise anydesired polarization direction by controlling, in phase and amplitude,the microwave energy supplied to the transmission-line networks, withthe additional advantage that cross-polarization is limited bycontrolling the balanced steering of the pairs of probes.

The multipatch antenna according to the invention is also preeminentlysuitable to be incorporated in a phased array antenna. FIG. 10 shows incross section a dielectric sheet 1 provided with radiating patches2(i,j), a metal plate 5 provided with holes 8(i,j) and probes 7(i,j). Inhis application, probes 7(i,j) are not fed by a transmission-linenetwork, but from phased array elements 15(i,j) which are in turn fed ina way well-known in the art for obtaining a radiation pattern withadjustable beam parameters. Also the connection of a probe 7(i,j) to aelectric circuit contained in the phased array element is well-known inthe art. The present embodiment is preeminently suitable for creatingsubarrays of for instance 8×8 phased array elements connected to 8×8radiating patches, each subarray then constituting a module in a phasedarray antenna system to be realised. Besides the extremely uncomplicatedconstruction, the present embodiment has the advantage of said largebandwidth. In addition it is also possible to provide each phased arrayelement with two probes. By feeding these probes at an adjustable phaseand amplitude, an adjustable polarization direction can be obtained,such in accordance with the description pertaining to FIG. 8. By feedingthese probes in opposite phase, a polarization direction with a very lowcross-polarization can be obtained, such in accordance with thedescription pertaining to FIG. 5 and FIG. 6.

By means of phased array elements 15(i,j) which are suitable for thebalanced feeding of two pairs of probes, as described with reference toFIG. 9, it is possible to analogously realise a phased array antennawith an adjustable polarization direction and a very lowcross-polarization.

Phased array elements 15(i,j) will usually be positioned in a backplane16, via which control signals, supply voltages, transmit-receive signalsand cooling are applied to the phased array elements. In this case themultipatch antenna shall be the final item in the assembly process,mounted from the front of the phased array antenna system. FIG. 11 showsa multipatch antenna according to the invention, suitable for frontmounting. In this figure, metal plate 5 is provided with connectors17(i,j), one for each probe 7(i,j) which is directly connected to thecorresponding connector 17(i,j). By providing corresponding phased arrayelement 15(i,j) with a counterpart 18(i,j) to connector 17(i,j), it ispossible for the multipatch antenna to be he final item in the assemblyprocess. In this respect it is advisable to select self-centringversions of connectors 17(i,j) and l8(i,j) and to divide the multipatchantenna into subarrays in order to reduce the forces acting duringassembly or disassembly of the multipatch antenna.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by letters patent of the United States is:
 1. A multipatch antenna comprising:an array of at least substantially equal radiators, positioned on one side of a dielectric sheet; a conductive ground plane positioned on the other side of the dielectric sheet; feeding means positioned near the ground plane on a side facing away from the dielectric sheet; and capacitive coupling means incorporated between the feeding means and the radiators for energizing the radiators; wherein the radiators each consist of one single radiating patch, positioned on an outer surface of the dielectric sheet and the capacitive coupling means comprise constant diameter conducting probes, on one side connected to the feeding means and on the other side ending in the dielectric sheet near the radiating patch, such that the ends of the conducting probes are completely embedded in the dielectric sheet.
 2. The multipatch antenna as claimed in claim 1, wherein the ground plane is provided with apertures at the location of the radiating patches to allow the passage of the probes.
 3. The multipatch antenna as claimed in claim 2, wherein the probes end near selected edges of the radiating patches for generating a radiation pattern with a selected polarization direction.
 4. The multipatch antenna as claimed in claim 3, wherein for each radiating patch, two probes are provided, both ending near opposite edges of the radiating patch.
 5. The multipatch antenna as claimed in claim 4, wherein the feeding means are arranged for feeding the two probes in opposite phases.
 6. The multipatch antenna as claimed in claim 5, wherein the antenna comprises a conformal array on a curved ground plane.
 7. The multipatch antenna as claimed in claim 4, wherein the antenna comprises a conformal array on a curved ground plane.
 8. The multipatch antenna as claimed in claim 3, wherein the antenna comprises a conformal array on a curved ground plane.
 9. The multipatch antenna as claimed in claim 3, wherein for each radiating patch, a first probe is provided for generating a radiation pattern with a first polarization direction and a second probe is provided for generating a second polarization direction which is at least substantially perpendicular to the first polarization direction.
 10. The multipatch antenna as claimed in claim 3, wherein for each radiating patch, a first pair of probes is provided for generating a radiation pattern with a first polarization direction and a second pair of probes is provided for generating a radiation pattern with a second polarization direction, the second polarization direction being at least substantially perpendicular to the first polarization direction.
 11. The multipatch antenna as claimed in claim 2, wherein the antenna comprises a conformal array on a curved ground plane.
 12. The multipatch antenna as claimed in claim 1 wherein the antenna comprises a conformal array on a curved ground plane. 